Seungheun Lee

An experimental study on coded excitation in CMUT arrays to utilize Simultaneous Transmission Multiple-zone Focusing method with frequency divided sub-band chirps

The frequency bandwidth of CMUTs (capacitive micromachined ultrasonic transducers) is known as relatively broader than that of other ultrasonic transducers. To utilize the wide bandwidth characteristic of the CMUT arrays, in this paper, we report on coded excitation techniques in the CMUT array. Through simulations, STMF (Simultaneous Transmit Multiple-zone Focusing) based ultrasound imaging techniques using orthogonally frequency-divided chirp signals are investigated. In the simulations, the frequency divided sub-band chirps that have orthogonal property are designed within the frequency bandwidth of the CMUT arrays, and simultaneously fired on multiple ranges, in which each signal is focused at a different range, in one transmission event. This paper also presents ultrasound images through a modulation and demodulation process of orthogonal sub-band coded signals. Experiments on the chirp-coded excitation in CMUT arrays are reported in this paper as a feasibility study of the FDMA (frequency division multiple access) like STMF method. In the experiment, mixed two orthogonal chirp signals are simultaneously fired with the CMUT arrays and the received signals are successfully separated into two compressed signals.

2D capacitive micromachined ultrasound transducer using novel tiling based on silicon frame

In this study, we showed the new transducer and probe integration of 2D ultrasound probe using cMUT. cMUT ultrasound probe having 8192 elements is assembled with tiling frame. Flip chip bonded cMUT-ASIC tiles were arrayed along 2×8 directions to enlarge lateral aperture. Tiling gap between two tiles was under 100μm. RTV layer that has 1mm thick is used in 2-D probe system as a lens and protection layer. Thermal module is also analyzed by using the thermal network analysis, which is realized with the air fans and the fins. Designed PCB circuit for tiling module which is considered with cooling spread concept is 5cm × 5cm dimension. Uniformity and performance of tiled ultrasound transducer were tested under soybean oil at 3MHz frequency successfully. The measured 256 elements distribution has only 4.45% deviation. If we can remove the side edge error, the deviation will be under 3%. The performance after RTV lensing showed 35% attenuation in Tx and 35~45% attenuation in Rx.

Hybrid beamformation for volumetric ultrasound imaging scanners using 2-D array transducers

In real-time 3-D ultrasound imaging using 2-D array transducers, manipulating massive ultrasound data acquired from a large number of system channels is a challenge as is interconnecting hundreds or thousands of elements of 2-D array with the imaging systems front-end electronics. Minimizing the number of transmitting and receiving elements and the firing events without degrading the spatial resolution is one of the solutions to reduce the overall system complexity and improve the frame rate. This paper introduces a new hybrid beamformation method for a medical image system. We also present an efficient 2-D array scanning method for miniaturized volumetric ultrasound imaging scanners. To evaluate our works, computer simulations are performed. From the simulation results, we have shown that the proposed hybrid beamforming method can provide comparable image quality to fully-sampled array beamformation, and the proposed method may be feasible for miniaturized real-time volumetric ultrasound scanners.

A feasibility study for arbitrary waveform generation using on-off pulses and modified PWM waveforms in the front-end circuit integrated with transducers

It is a challenge to implement the arbitrary waveform generator (AWG) with high performance devices such as digital to analog converters (DACs) and linear power amplifiers (LPAs) in the front-end circuits which should be integrated with array transducers due to its issue in size and power consumption. Over the past several decades, a number of approaches using only on-off pulses have been proposed to transmit an arbitrary waveform. A pulse width modulation (PWM) technique is one of the approaches to simplify the implementation of AWG into the transmitter. In this paper, a preliminary study for an arbitrary waveform generation, which is essential for the coded excitation imaging, using only on-off pulses is introduced. In this study, we propose a proof of concept of an adapted PWM waveform using uni-polar and bi-polar pulses. In theoretical and simulation studies, transmission signals using uni-polar and bi-polar pulses, and the PWM waveforms are analyzed and investigated in terms of a frequency characteristic and a transmission power efficiency (TPE) that indicates the pulse-shaping performance of the generated waveform by defining the ratio of its output and input power through a given transducer. The results demonstrate the possibility to perform the arbitrary waveform generation with the transmitter architecture using only on-off pulses and the PWM waveforms without any DAC and LPA.